The interior spaces of buildings are often at a lower than desired level of humidity. This situation occurs commonly in arid climates and during the heating season in cold climates. There are also instances in which special requirements exist for the humidity of interior spaces, such as in an art gallery or where other delicate items are stored, where it is desired that the interior humidity levels be increased above naturally occurring levels. Therefore, humidifier systems are often installed in buildings to increase the humidity of an interior space.
Humidification systems may take the form of free-standing units located within individual rooms of a building. More preferably, humidification systems are used with building heating, ventilation, and air conditioning (HVAC) systems to increase the humidity of air within ducts that is being supplied to interior building spaces. In this way, humidity can be added to the air stream at a centralized location, as opposed to having multiple devices that increase humidity at multiple points within the building interior. Additionally, because the air within ducts may be warmer than the interior space air during a heating cycle, the additional air temperature can help prevent water vapor from condensing in the vicinity of the humidifier, such as on the inside of the duct.
An issue associated with humidification system is that they should only discharge water vapor into a duct and not liquid water. Liquid water within a duct can create a number of serious problems. For example, liquid water that remains stagnant within a duct can promote the growth of mold or organisms that can release harmful substances into the air flow, potentially causing unhealthy conditions in the building. Liquid water can also cause rusting of a duct which can lead to duct failure, and can create leaks from the duct to the building interior spaces which are unsightly, can cause a slipping hazard, and can lead to water damage to the structure.
One known humidification method involves direct steam injection into an air duct of a building. This approach is most commonly used in commercial buildings where a steam boiler is present to provide a ready supply of pressurized steam. Steam humidification has the advantage of having a relatively low risk of liquid moisture entering a duct or other building space. However, pressurized steam injection systems are associated with a risk of explosion of the steam pressure vessels, as well as a risk of possibly burning nearby people, both of which are very serious safety concerns. In residential applications, there are usually no readily available sources of pressurized steam. An open bath humidifier system may be used, however these are difficult to install because they require a large hole in the duct and can only be used with horizontal or upflow ducts. Alternatively, a residential application may use direct steam injection, but this requires a separate unit to generate pressurized steam and this separate unit is costly. Moreover, the system would suffer from the same disadvantages as are present in commercial direct steam injection systems.
One type of humidifier that is commonly used in residential applications that has the advantages of steam humidification without the need for a separate source of pressurized steam is a tank heater type humidifier. In this type of humidifier, heat is generated within a tank of water, causing the water to boil and steam to be generated. The heat input may be any of a number of different sources, however, commonly an electrical heating element is used. One problem associated with this type of humidifier is that as water is boiled off as steam, the impurities in the water remain in the tank. These impurities generally include minerals that are naturally occurring in most sources of water. Over time, the concentration of these impurities will tend to increase in the tank, leading to greater amounts of impurities that solidify and deposit on the surfaces inside the tank. These deposits can accumulate to the point of creating numerous problems. For example, deposits on a heating coil reduce the heat transfer rate to the water, resulting in lower steam production and possibly causing overheating and failure of the coil. Deposits in the tank can clog passages where water or steam flows in or out, resulting in the failure of the humidifier.
Improved humidification systems are desired. In particular, improved techniques for detecting accumulation of deposits and obstructions within a humidifier are needed.